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Scalability Analysis of a LoRa Network under Imperfect Orthogonality
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Systems and Technology. (Communication Systems and Networks (CSN))ORCID iD: 0000-0003-3717-7793
University of Brescia, Italy. (Communication Systems and Networks /CSN))
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Systems and Technology. (Communication Systems and Networks (CSN))
Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Systems and Technology. (Communication Systems and Networks (CSN))
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2019 (English)In: IEEE Transactions on Industrial Informatics, ISSN 1551-3203, E-ISSN 1941-0050, Vol. 15, no 3, p. 1425-1436Article in journal (Refereed) Published
Abstract [en]

Low-power wide-area network (LPWAN) technologies are gaining momentum for internet-of-things (IoT) applications since they promise wide coverage to a massive number of battery-operated devices using grant-free medium access. LoRaWAN, with its physical (PHY) layer design and regulatory efforts, has emerged as the widely adopted LPWAN solution. By using chirp spread spectrum modulation with qausi-orthogonal spreading factors (SFs), LoRa PHY offers coverage to wide-area applications while supporting high-density of devices. However, thus far its scalability performance has been inadequately modeled and the effect of interference resulting from the imperfect orthogonality of the SFs has not been considered. In this paper, we present an analytical model of a single-cell LoRa system that accounts for the impact of interference among transmissions over the same SF (co-SF) as well as different SFs (inter-SF). By modeling the interference field as Poisson point process under duty-cycled ALOHA, we derive the signal-to-interference ratio (SIR) distributions for several interference conditions. Results show that, for a duty cycle as low as 0.33%, the network performance under co-SF interference alone is considerably optimistic as the inclusion of inter-SF interference unveils a further drop in the success probability and the coverage probability of approximately 10% and 15%, respectively for 1500 devices in a LoRa channel. Finally, we illustrate how our analysis can characterize the critical device density with respect to cell size for a given reliability target.

Place, publisher, year, edition, pages
2019. Vol. 15, no 3, p. 1425-1436
Keywords [en]
IoT, low-power wide-area networks, LoRaWAN, interference, stochastic geometry
National Category
Communication Systems Telecommunications Computer Engineering
Identifiers
URN: urn:nbn:se:miun:diva-34280DOI: 10.1109/TII.2018.2864681ISI: 000460580100018Scopus ID: 2-s2.0-85051371604OAI: oai:DiVA.org:miun-34280DiVA, id: diva2:1240094
Projects
TIMELINESSSMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Funder
European Regional Development Fund (ERDF)Knowledge FoundationAvailable from: 2018-08-20 Created: 2018-08-20 Last updated: 2019-10-16Bibliographically approved
In thesis
1. Low Power Wireless Technologies for IIoT: Analysis and enhancement of communication delay, reliability and scalability
Open this publication in new window or tab >>Low Power Wireless Technologies for IIoT: Analysis and enhancement of communication delay, reliability and scalability
2019 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

In recent years, the implementation of wireless communication systems in industrial environments has significantly increased. As a result, new applications such as Industrial Internet-of-Things (IIoT) have arisen, reshaping the future of industrial automation. Industrial environments, however, pose a demanding challenge for the implementation of wireless communication systems. IIoT applications have very stringent Quality of Service (QoS) requirements, in particular regarding energy consumption, timeliness, and reliability; and failing to fulfill the requirements could result in costly and dangerous system faults. Ranging from short to long range, the wide set of possible application cases within IIoT is based on different wireless technologies designed to excel in a certain scenario. A common aspect of these applications is the presence of energy-limited devices, and as a result, the development of low power technologies is becoming increasingly more important.

In this thesis, three specific low power wireless technologies are analyzed: Bluetooth Low Energy (BLE), Bluetooth Mesh, and LoRa. These three protocols target short, mid and long-range communication, respectively, thus providing the opportunity of exploring a wider set of application cases. The overall purpose of this thesis is to contribute to an extensive and well-rounded understanding of how these three technologies perform in terms of the scalability, reliability, and transmission delay. In particular, the aim is to determine their suitability for IIoT and to identify the key elements within their functional schemes that can be optimized to achieve improved performance.

The first part of the thesis explores the potential of BLE meeting real-time demands found in the domain of short-range IIoT. In order to evaluate the suitability of the protocol for these scenarios, we present an analytical model of the delay performance of BLE for connection-oriented configurations. We studied the effect of possible adaptations in the retransmission scheme on reliability and timeliness performance. Different retransmission schemes are evaluated and simulation results proved that by optimally modifying the BLE retransmission model, a maximum delay below 46 ms and a packet loss rate in the order of 10−5can be obtained. Therefore, BLE proved to be capable of fulfilling the requirements of even the most demanding cases within the considered range of applications.

The second part of the thesis evaluates the QoS performance and limitations of the recently released Bluetooth Mesh protocol through extensive simulations. We analyzed the impact of choosing different configurations of the protocol parameters on the end-to-end scalability, reliability and delay performance. In particular, we focused on the configuration of the Advertising Events and Scanning Events timing, including the ScanInterval and TinterPDU . Results revealed that the TinterPDU has to be chosen accordingly with the scanInterval and that it significantly impacts the end-to-end delay and reliability. Due to the flooding approach, larger TinterPDU resulted in a higher end-to-end packet loss rate. We demonstrated that, by introducing randomization in the time parameters, the reliability and delay performance can be greatly improved. It was also shown that the achievable average delay is relatively low, of around 250ms over 10 hops under the worst simulated network conditions. However, we observed that scalability is especially challenging for Bluetooth Mesh since it is particularly vulnerable to broadcast storm, hindering the communication reliability for denser deployments.

The third part of the thesis focuses on Low-Power Wide-Area Networks (LPWANs), in which LoRaWAN, with its physical (PHY) layer design and regulatory efforts, has emerged as a widely adopted solution. By using chirp spread spectrum modulation with quasi-orthogonal spreading factors (SFs), LoRa PHY offers coverage to wide-area applications while supporting a high density of devices. We present an analytical model of a single-cell LoRa system that accounts for the impact of interference among transmissions over the same SF (co-SF) as well as different SFs(inter-SF). The latter is a result of the imperfect orthogonality of the SFs. By modeling the interference field as a Poisson point process under duty-cycled ALOHA, we derived the signal-to-interference ratio (SIR) distributions for several interference conditions. Results indicate that, for a duty cycle as low as 0.33%, the network performance under co-SF interference alone is considerably optimistic, as the inclusion of inter-SF interference unveils a further drop in the success probability and the coverage probability of approximately 10% and 15%. In conclusion, we illustrate how our analysis can characterize the critical device density with respect to cell size for agiven reliability target.

Place, publisher, year, edition, pages
Sundsvall: Mid Sweden University, 2019. p. 80
Series
Mid Sweden University licentiate thesis, ISSN 1652-8948 ; 158
National Category
Engineering and Technology
Identifiers
urn:nbn:se:miun:diva-36202 (URN)978-91-88947-04-8 (ISBN)
Presentation
2019-06-10, M102, Sundsvall, 13:00 (English)
Opponent
Supervisors
Projects
SMART (Smarta system och tjänster för ett effektivt och innovativt samhälle)
Note

Vid tidpunkten för framläggningen av avhandlingen var följande delarbete opublicerat: delarbete 3 manuskript.

At the time of the defence the following paper was unpublished: paper 3 manuscript.

Available from: 2019-05-23 Created: 2019-05-22 Last updated: 2019-06-13Bibliographically approved

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Mahmood, AamirGuntupalli, LakshmikanthRondón, RaúlGidlund, Mikael

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